/**
* Converts a string to uppercase, returning the result.
*
* The argument can be any expression as long as it resolves to a string.
*
* @see http://docs.mongodb.org/manual/reference/operator/aggregation/toUpper/
* @see Expr::toUpper
* @param mixed|Expr $expression
* @return self
*/
public function toUpper($expression)
{
$this->expr->toUpper($expression);
return $this;
}
